Abstract
Background : Leishmania (L) are intracellular protozoan parasites that are able to survive andreplicate within the harsh and potentially hostile phagolysosomal environment of mammalianmononuclear phagocytes. A complex interplay then takes place between the macrophage (MΦ)striving to eliminate the pathogen and the parasite struggling for its own survival.To investigate this host-parasite conflict at the transcriptional level, in the context of monocyte-derived human MΦs (MDM) infection by L. major metacyclic promastigotes, the quantitativetechnique of serial analysis of gene expression (SAGE) was used. Results : After extracting mRNA from resting human MΦs, Leishmania-infected human MΦs and L.major parasites, three SAGE libraries were constructed and sequenced generating up to 28,173;57,514 and 33,906 tags respectively (corresponding to 12,946; 23,442 and 9,530 unique tags). Usingcomputational data analysis and direct comparison to 357,888 publicly available experimentalhuman tags, the parasite and the host cell transcriptomes were then simultaneously characterizedfrom the mixed cellular extract, confidently discriminating host from parasite transcripts. Thisprocedure led us to reliably assign 3,814 tags to MΦs' and 3,666 tags to L. major parasitestranscripts. We focused on these, showing significant changes in their expression that are likely tobe relevant to the pathogenesis of parasite infection: (i) human MΦs genes, belonging to keyimmune response proteins (e.g., IFNγ pathway, S100 and chemokine families) and (ii) a group ofLeishmania genes showing a preferential expression at the parasite's intra-cellular developing stage. Conclusion: Dual SAGE transcriptome analysis provided a useful, powerful and accurate approachto discriminating genes of human or parasitic origin in Leishmania-infected human MΦs. The findingspresented in this work suggest that the Leishmania parasite modulates key transcripts in humanMΦs that may be beneficial for its establishment and survival. Furthermore, these results providean overview of gene expression at two developmental stages of the parasite, namely metacyclicpromastigotes and intracellular amastigotes and indicate a broad difference between theirtranscriptomic profiles. Finally, our reported set of expressed genes will be useful in future roundsof data mining and gene annotation